i think the a spelling is more common but like others said once they know, no excuses they should get it right! im big on getting the correct spelling for names if im writing an invite, card etc.
Most names people are going to get wrong even the simple ones.
i get Nichole, Nixon has been spelt Nixson, nickson so far and Tyron ofcourse gets a lot of Tyrone (with that pronounciation which its not)
Zachery is unique!!